(1) Field of the Invention:
This invention relates to an easily water-dispersible pigment composition, and more specifically to a pigment composition dispersible readily by its addition to alkaline water and subsequent slight mixing and hence useful, especially, for the preparation of water-base inks and water-base paints.
(2) Description of the Prior Art:
A number of proposals have heretofore been made on pigment compositions each of which can be readily dispersed by adding same in an aqueous medium or vehicle and then merely mixing the resultant aqueous mixture. These readily-dispersible prior-art pigment compositions are generally mixtures of pigments and surfactants kneaded together or mixtures of pigments and water-soluble polymers kneaded together.
Readily-dispersible conventional pigment compositions of the above-mentioned sort employ the surfactants or water-soluble polymers in relatively large amounts relative to their corresponding pigments so that they can be readily dispersed in aqueous media or vehicles. Where the pigment is an organic pigment, a surfactant or water-soluble polymer is used in an amount accounting for at least 40 wt. % of a pigment composition to be prepared. When such a readily-dispersible pigment composition is added and dispersed in an aqueous medium or vehicle for use in the preparation of a water-base ink or water-base paint, one or more of various polymers are also used as binders in addition to the pigment composition. These polymers are selected suitably depending on what use to be made of the resulting water-base ink or paint. Since surfactants or water-soluble polymers are contained in high proportions in their corresponding pigment compositions, these surfactants or water-soluble polymers amount to significant proportions in dispersions and affect deleteriously on the properties of polymers incorporated as binders, resulting in development of various problems. These problems can be solved by lowering the proportion of a surfactant or water-soluble polymer to be employed in a pigment composition. Use of such a surfactant or water-soluble polymer in any amounts below 40 wt. % will however lead to significant loss of the high dispersibility of the pigment in the pigment composition so that sufficient dispersion will no longer be attained by its simple mixing in an aqueous medium or vehicle.
Under the circumstances, there is thus a strong demand for an easily-dispersible pigment composition which contains a dispersant in such a small amount that the properties of a resin added as a binder in an aqueous medium or vehicle are not deleteriously affected.